Is sugar really toxic?

Recently, headlines including "Tax and regulate sugar like alcohol and tobacco, urge scientists" (Guardian, 1 February 2012), "Sugar 'is toxic and must be regulated just like cigarettes', claim scientist” (Daily Mail, 2 February 2012) and “The bitter truth about sugar” (Sunday Telegraph Magazine, 25 March 2012) have hit the news. So, is it true? Is sugar really harmful to our health, or worse – toxic?

What research is this based on?

These headlines were in response to an article ‘The toxic truth about sugar’, published on 2 February 2012 in Nature, in which three U.S. scientists discussed the purported role that sugar plays in the development of chronic diseases such as heart disease. The title of the article itself implies that sugar is ‘toxic’ – a very strong statement that fuelled many of the media headlines.

It is important to highlight that the article in Nature, rather than being a scientific paper (as it was often referred to in the press), was a commentary authored by Robert H. Lustig and colleagues from the University of California. Robert Lustig is Professor of Clinical Paediatrics in the Department of Pediatrics and the Centre for Obesity Assessment, Study and Treatment at the University of California. As a commentary, the paper does not present any new science nor is it a scientific review of the evidence; it is the authors’ own opinion. Although Lustig and colleagues do refer to a few, selected scientific papers in their article to support their claims, they mainly rely for support on one of Lustig’s own papers, in which he investigates the metabolism of fructose in the body (Lustig 2010). Lustig and colleagues do not summarise or critique major reviews on sugar and its association with diet-related diseases undertaken around the world.

Two recent major scientific reviews found insufficient evidence to support a link between total sugar intake and obesity (although there is some evidence suggesting sugar-sweetened beverages may increase the risk of obesity), blood cholesterol levels, metabolic syndrome, heart disease or cancer and so do not support the claims made by Lustig et al. (European Food Safety Authority (EFSA) 2010; Hauner et al. 2012). The findings of these reviews are consistent with the findings of the UK advisory committee, COMA, dating back to 1989 (Department of Health (DH) 1989).

A recent systematic review of the science on carbohydrate and health by the German Nutrition Society (Hauner et al. 2012) concluded that evidence does not show a link between sugar intake and the development of type 2 diabetes, although the authors suggested a ‘possible’ link between sugar-sweetened beverages and the condition. This review concluded that the available evidence did not support a link between long-term intake of fructose or sucrose and increased blood pressure and that the evidence for an association with obesity was insufficient for all types of sugar, although there is some evidence of a link between sugar-sweetened beverages and obesity. The European Food Safety Authority (EFSA) concluded in its major review that evidence relating high intake of sugars, compared to high intake of starch, to weight gain is inconsistent for foods, but that there is some evidence that high intakes of sugars in the form of sugar-sweetened beverages might contribute to weight gain. EFSA suggested there are limited, and mainly short-term, data on the effects of high intake of sugars on glucose and insulin response.

The authors of the Nature article also claim that obesity is not a cause of chronic diseases including heart disease, diabetes and cancer. This statement is not backed by science; obesity has been found to be an independent risk factor for heart disease, diabetes and some types of cancer (WHO 2003; World Cancer Research Fund & American Institute for Cancer Research 2007).

Lustig and colleagues also dismiss the role of fat and saturated fat in association with heart disease and other chronic diseases, saying that “most medical professionals no longer believe that fat is the primary culprit”. Yet, evidence shows that there is a relation between high fat consumption and energy density (calorie content per gram of food) of the diet, and that consumption of an energy-dense diet increases the risk of obesity (and therefore the risk of some chronic diseases) (WHO 2003).

Overall, evidence does not support the claims made that sugar increases the risk of diseases like obesity, diabetes and heart disease.

Is fructose really as bad as alcohol?

One particular sugar highlighted by Lustig and colleagues is fructose, the sugar found naturally in fruit. They claim that “fructose can trigger processes that lead to liver toxicity and a host of other chronic diseases” and that “a little is not a problem, but a lot kills”. These claims are based on Lustig’s own paper published in the Journal of the American Dietetic Association in 2010, in which an aim was to consider parallels between fructose and ethanol metabolism.

When investigating the metabolism of fructose in the body, the author relies heavily on animal studies and clinical human studies that generally use large doses of pure fructose. Although such studies give a useful insight into the metabolism of fructose, they do not reflect a real life picture of the role of fructose in our diet. Though there is some evidence that high intakes of fructose may negatively affect human metabolism, it is difficult to draw conclusions on the effect of fructose contained in sucrose and other sweeteners on health and evidence does not support the claim that fructose, at the levels generally consumed in our diets, is damaging to the body in a similar way to alcohol.

Has our sugar intake risen?

In their article, Lustig and colleagues claim that sugar consumption worldwide has tripled over the past 50 years (although they do not provide a reference to support this). They also cite the high level of use of high-fructose corn syrup (HFCS) as being one of the key problems, particularly in the US. HFCS is not currently in wide use in Europe but this situation may change. UK data do not support the claim that sugar intakes have significantly increased; in fact, data show that sugar consumption has not varied greatly over several decades. Total sugar intake in adult men was 115 g per day in 1986/87, 119 g per day in 2000/01 and 110 g per day in 2008-2010. Total sugar intake in adult women was 86g per day in 1986/87, 89 g per day in 2000/01 and 88 g per day in 2008-2010. Intake of non-milk extrinsic sugars (NMES), which include added sugars, in adult men was 78 g per day in 2000/01 and 72 g per day in 2008-2010. Intake of NMES in adult women was 52 g per day in 2000/01 and was the same in 2008-2010 (Bates et al. 2011; Henderson et al. 2003; Gregory et al. 1990).

Is sugar really addictive?

Lustig and colleagues argue that sugar has “dependence-producing properties”. A review published in Nutrition Bulletin does not support the claim that sugar (or fat) is an addictive substance. Although the authors of the review acknowledge hedonistic responses to the consumption of sweet foods, which is the pleasure we get from eating such foods, the authors concluded that “sugar and sweets do not appear to meet the current criteria for substance dependence as formulated in the Diagnostic and Statistical Manual of Mental Disorders – Fourth Edition (DSM IV)” (Drewnowski & Bellisle 2007).

In summary

Current evidence does not support the dramatic claims about the association between sugar and health made by Lustig and colleagues. Sugar is a source of energy in our diet and it is certainly not ‘toxic’ in the amounts on average consumed in the UK and other European countries. Eating too much energy from any of the macronutrients (fat, protein, carbohydrate (starchy carbohydrates and sugar) over time will lead to weight gain and may have a negative impact on health, because obesity has been found to be a risk factor for various chronic diseases.

Overall, the commentary by Lustig and colleagues, published in Nature, does not reflect the current state of evidence around sugar and its association with chronic disease, as shown in some recent major systematic reviews. The authors also mainly focus on the situation in the U.S., which does not reflect the situation in the UK, e.g. in terms of consumption of HFCS. Food-based guidelines, such as the Department of Health’s Eatwell plate, suggest that foods and drinks that are high in sugar and/or fat should be consumed in limited amounts, but there is no need to completely cut these foods out of a healthy and balanced diet.

'Is sugar really that bad for you?’ - FREE download available in 11 different languages

In response to the publication of the commentary, BNF published a Facts Behind the Headlines article ‘Is sugar really that bad for you?’ in Nutrition Bulletin (June 2012). This article has been made free to download and it has been translated into 10 other languages: Czech, Greek, German, Spanish, French, Hungarian, Italian, Polish, Portuguese and Slovak.

The original article and its accompanying translations can be found here.